Remote operation of optical system

ABSTRACT

A method and apparatus for controlling a detector array based optical system using reflected or transmitted light for machine vision is disclosed. The light characteristic such as power (intensity) or distribution of power received by said optical system is detected and an electrical signal indicative of the characteristic is transmitted to a remote control system. The control system then adjusts a light power related variable of the optical system when the received light characteristic signal is deficient. A method and apparatus for linearizing the output of a diode array is also disclosed. An element correction array is set up in a microprocessor and an encoding device providing precise edge movement data is moved past the elements of the diode array so that the data from the encoder and from the diode array can be compared and the difference inputted as offset values for the corresponding positions of the elements in the correction array. Thereafter, during operation, the offset values are added to the diode array element reading to obtain a corrected diode array output which is substantially linear.

This is a division of application Ser. No. 454,989 filed Jan. 3, 1983,now USP 4,692,884 .

FIELD OF THE INVENTION

The present invention relates generally to the operation of vision formachines, and more particularly to a control system and outputlinearization of optical detector arrays.

BACKGROUND OF THE INVENTION

Detector array based optical systems for industrial inspection andmachine guidance (machine vision) have been utilized. However, someproblems do exist. A major problem is often related to light power. Thisis caused by a number of problems such as degradation of the lamps andaccumulation of dirt or debris on windows, optics, parts, and others.Problems of this sort can be solved by building observed light powerdetectors into the system to compensate lamp power, array intergrationtime, or scan rate as a function of detected power through the window bythe sensor unit.

However, many times the source of error also couples with a change inthe object being viewed. For example, where a part is being viewed bythe machine, the part color can change due to a different castingsupplier, parts running oily, or a faulty parts washer which leaves dirtor a wash residue on the part. In such situations, it is not sufficientto make a simple light level change since it is not known what thecorrect reflecting light level from the part should be. For example, ifan operator uses a clean and dry master which is shiny to set thecontrol system for the optical sensor, and the parts are dull, dirty orwet, incorrect settings of the optical system result.

In large range dimensional optical sensors, the sensor output is oftennonlinear. It is therefore necessary to calibrate this output todetermine the correct dimension. This is often difficult to do.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and apparatus forcontrolling a detector array based optical system for machine vision isdisclosed. The light characteristic such as power (intensity) or spacialdistribution of power received by the array based optical system isdetected and an electrical signal indicative of this light power istransmitted to a remotely located control system. When the receivedlight characteristic signal is deficient, the control system adjusts asuitable light variable of the optical system so that a sufficient lightcharacteristic signal is achieved.

Typically, the optical system variable which is adjusted is selectedfrom the detector array scan rate, the array integration time, or thelight output level. In addition, the diode array calibration points, thediode array threshold limit, the diode array dump timing, themeasurement limits of the optical system, and the color sensitivity arealso light power output variables which can be adjusted by the controlsystem. The control system can also adjust the movement of the objectwhich is being viewed by the optical system by changing the rate ofmovement or the dwell time of the object. A blow-off device for thewindow of the array or the object being detected can also be controlledby the control system to remove debris which is adversely affecting thelight characteristic.

In the preferred embodiment the control system includes a computer whichis suitably programmed to perform the desired adjustments. This computerprogram is remotely located from the detecting array and can beconnected over telephone lines if it is desired to locate the controlsystem in a separate building, or at a vendor plant in a distant cityfor example.

In order to linearize the output of a diode array, a microprocessor hasa memory in which an element correction array corresponding to the diodearray is provided. An encoding device is used to input precise edgemovement data to the microprocessor as an object is moved past theelements of the diode array. The data from the encoding device and thediode array at each element are compared and the difference is inputtedinto the microprocessor as offset values at the corresponding positionsin the element correction array. Thereafter, the correction array offsetvalue is added to each corresponding diode array element reading duringoperation of the system. This produces a substantially linear outputfrom the diode array. Conveniently, the microprocessor is remotelylocated from the diode array and signals are transmitted between thetwo. The linearization data in the correction array can be recalculatedperiodically by a signal from the remotely located microprocessor.

With the present invention, the remote operation of an optical systemcan be advantageously effected by skilled personnel quickly andefficiently. In addition, the control system disclosed incorporates manymaintenance features into the optical system which allow easy troubleshooting with the computer via remote telephone lines.

Other features and advantages of the present invention are stated in orare apparent from a detailed description of presently preferredembodiments of the invention found hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a control system for a detectorarray based optical system according to the present invention.

FIG. 2 is a schematic representation of an apparatus for linearizing theoutput of a diode array according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the drawings in which like numerals represent likeelements, a control system 10 for a detector array 12 of an opticalsystem 14 is disclosed. Optical system 14 is, typically, used formachine vision in an industrial operation where an object 16 is detectedby array 12 using light from a source 18 reflected off object 16.

Associated with detector array 12 is a monitor 20 which monitors one ormore characteristics of detector array 12, and the associated system.Among these characteristics are: light power of light source 18,received light power, array clock rate, array integration time, arraycalibration points, array threshold levels, array dump timing,measurement limits, and (if applicable) camera color sensitivitysettings. Monitor 20 is connected to a vision control 22 for opticalsystem 14. Vision control 22 is also connected to a changer means 24which is capable of changing any of the monitored characterisitcs.Vision control 22 is further connected to a control computer 26 whichcontrols the operation of vision control 22.

Control computer 26 may also be connected to a machine control 28 whichcontrols the movement of object 16. A monitor 30 is connected to machinecontrol 28 and is used to monitor characteristics relating to themovement of object 16. Among these characteristics monitored are rate ofmovement and dwell at a station. Also connected to machine control 28 isa changer mean 32 which is capable of changing the characteristicsmonitored by monitor 30.

In a large industrial operation, control computer 26 is convenientlyconnected to a central plant computer 34. Plant computer 34 is used tocontrol the operation of a number of related operations including theoperation controlled by control computer 26. Plant computer 34 is inturn connected to a remote computer 36. Remote computer 36 canconveniently be located a large distance from plant computer 34 forexample, from a host plant where highly skilled personnel monitor theoperation of plant computer 34 and optical system 14 in particular.Conveniently, this is done over telephone lines 38 by use of modems 40and 42. It should also be realized that remote computer 36 can bedirectly attached to control computer 26, bypassing plant computer 34,by use of a line 44 where remote computer 36 is in the same building ascontrol computer 26, or via line 46 attached to modem 40.

In operation, control system 10 functions in the following manner.Initially, monitor 20 is used to monitor the light power or distributionof power received by detector array 12 from light reflected off ofobject 16 and originating at light source 18. A signal indicative ofreceived light power is then transmitted to vision control 22, controlcomputer 26, and ultimately to remote computer 36. As discussed above, anumber of factors can cause the received light power to fall below adesired level. Among these factors are a change in light source power ordistribution due to age or replacement, or a change in object 16 such asa color change, oil on object 16, or dirt or wash residue which shouldnot be present on object 16. Therefore, even though the light powerreceived by detector array 12 is less than desired, it may be that theoperation of optical system 14 is still possible but some of thecharacteristics need to be changed. Therefore, remote computer 36 isactivated to change one or more characteristics of detector array 12 viachanger means 24, or the machine via changer means 32. Conveniently, adiagnostic program in remote computer 36 actually trouble shoots opticalsystem 14 and makes the appropriate changes to the characteristics whichare appropriate. It should be noted that the location of remote computer36 in, for example, a host plant allows a highly skilled person to takeimmediate action to make the changes necessary which may solve theproblem. The changes necessary can be effected through vision control 22or machine control 28 as described above.

By way of example, consider the case where object 16 has some amount ofdirt or the like on its surface. This dirt causes the reflected lightfrom light source 18 to be decreased and the received light power atdetector array 12 is subsequently much reduced. As monitor 20 sensesthis, a signal is sent to vision control 22, control computer 26, andultimately to remote computer 36. Upon receipt of this signal, remotecomputer 36 attempts to correct the problem by changing one or more ofthe light power output or detector array characteristics. In order tosolve this problem, the intergration time of detector array 12 could bevaried. In addition, the scan widths or threshold limits could be openedup to allow operation to continue until changes are made in object 16.

Besides dirt on object 16, it is also possible for dirt or debris toaccumulate on the window of detector array 12. If such a situation islikely, changer means 24 and 32 could also control blow-off deviceswhich would direct a jet of air against the window of detector array 12or object 16, respectively. This could be the first remedial actionattempted by remote computer 36 upon the receipt of a low power outputsignal.

By use of control system 10, it is possible to detect the light powerreceived and to change or adjust various light characteristic variablesas necessary. In addition, control system 10 is also advantageously usedto reset the light characteristic variables at the beginning of eachday's production. This is done be running a few characteristic objects16 from the day's production through optical system 14 to get asignature of object 16. Remote computer 36 then sets the various lightpower output variables at the optimal values. All this could be donelocally at optical system 14 by use of twisting pots or the like, butthe use of remote computer 36 allows such changes to be madeautomatically with the use of diagnostic programs which are moreeffecient and which actually make the changes themselves. In addition,remote computer 36 continues to monitor the light power output and tomake any subsequent changes which may be necessary.

It should also be appreciated that the use of a remote computer 36allows one to have a completely automated system, whereby all of theinspection and robot camera sensors in a particular system which dependon light level can be set automatically by remote computer 36. Whilethis is an extreme case, it does make possible the "fully computerizedfactory of the future".

Depicted in FIG. 2 is an output linearization system 50 for a diodearray 52. Linearization system 50 includes an encoder 54 which isoperatively associated with diode array 52 and a remotely locatedmicroprocessor 56. Linearization system 50 is particularly useful withlarge range detector array systems in order to achieve maximum accuracy.In this context, it is highly desirable to analyze or vary the state ofcalibration of diode array 52 remotely.

Linearization system 50 functions in the following manner. Initially,the memory of microprocessor 56 is set up with an element correctionarray having the same number of array elements as diode array 52. Forexample, for a 1024 element sensor in diode array 52, a 1024 correctionarray is set up in microprocessor 56. Encoder 54 is then used to provideprecise edge movement data as an object edge is moved through the fieldof view of diode array 52. Microprocessor 56 compares the data fromencoder 54 with the data from the various elements of diode array 52.The difference between the two readings is the value by which theelements in diode array 52 are offset from having a linear output. Thisoffset value for each element of diode array 52 is inputted into thecorresponding element of the correction array in microprocessor 56. Thiscompletes the linearization process for diode array 52, which isperformed as often as is necessary. It should be noted that thislinearization is performed remotely, and can be performed by amicroprocessor located in another plant by using suitable transmissionmeans such as disclosed with respect to the embodiment described in FIG.1.

After the calibrating procedure described above, in the gauging mode asan object is moved across the field of view of diode array 52, theelements of diode array 52 produce raw data which is fed tomicroprocessor 56. The location or elements from which the raw dataoriginated is then determined and the corresponding element offset valuein the element correction array in microprocessor 56 is then added tothe raw data from each element. This causes the raw data from eachelement of diode array 52 to be corrected so that a linear data outputis produced. This linearized data or corrected data is then outputted bymicroprocessor 56 to be further processed by the control system withwhich diode array 53 is associated.

It is further noted that the machine changer 32 may be used to slow downthe part movement, produce longer dwell in station, etc. to allow morelight to be received by the detector array within a given integrationtime making up for loss of light power due to dirty objects or windowsfor example. In addition, such a slowdown allows in general more scansto be made, increasing the chance of obtaining good data in the presenceof contamination or other adverse variables.

It is also noted recalibration of detector arrays can also be done usingthe control system here described to suit new conditions such as lightsize change.

Note that "light" includes UV, IR and visible wavelengths ofelectro-magnetic radiation.

While the present invention has been described with respect to exemplaryembodiments thereof, it will be understood by those of ordinary skill inthe art that these and other variations and modifications can beeffected within the scope and spirit of the invention.

I claim:
 1. A control system for a detector array based optical systemused for machine vision which optical system has a detector array whichreceives light from a plurality of succeedingly presented objects,comprising:a transmitting means for transmitting signals between acontrol device and the optical system; a detecting means for detecting alight characteristic of the light received by the detector array duringuse on a presented object and for transmitting a signal indicative ofsaid light characteristic via said transmitting means to the controldevice; and an adjusting means for adjusting a light characteristicvariable of said optical system for the succeeding objects when thereceived light characteristic for at least one of the previous objectsis deficient.
 2. A control system as claimed in claim 1 wherein saidadjusting means adjusts a light characteristic variable which is one ofdetector array scan rate, integration time, and light output level of alight source.
 3. A control system as claimed in claim 2 wherein saiddetecting means also detects and wherein said adjusting means alsoadjusts detector array calibrations.
 4. A control system as claimed inclaim 3 wherein said detecting means also detects and wherein saidadjusting means also adjusts detector array threshold limits.
 5. Acontrol system as claimed in claim 4 wherein said detecting means alsodetects and wherein said adjusting means also adjusts the detector arraydump timing.
 6. A control system as claimed in claim 5 wherein saiddetecting means also detects and wherein said adjusting means alsoadjusts measurement limits of the optical system.
 7. A control system asclaimed in claim 5 wherein said optical system includes a colorsensitivity camera, wherein said detecting means detects and saidadjusting means adjusts the color sensitivity.
 8. A control system asclaimed in claim 2 wherein the machine vision is of a moving element,and wherein said detecting means also detects and said adjusting meansalso adjusts the rate at which the element moves.
 9. A control system asclaimed in claim 2 wherein the machine vision is of a moving elementwhich is stopped for a period of time, and wherein said detecting meansalso detects and said adjusting means also adjusts the dwell time of thestopped element.
 10. A control system as claimed in claim 2 wherein saidadjusting means includes a blow-off means for directing a jet airagainst the window of the detector array to clean light obscuring debrisfrom the window.
 11. A control system as claimed in claim 10 whereinsaid blow-off means also directs a jet of air against an object beingviewed to clean non light reflecting debris from the object.
 12. Acontrol system as claimed in claim 2 and further including computermeans for initially receiving the detected light characteristicvariables produced by a sample operation of the optical system and fordetermining appropriate values for the variables which are thenautomatically adjusted in the optical system by said adjusting means.13. A control system as claimed in claim 12 wherein said transmittingmeans includes modem means for transmitting the signals over telephonelines from said detecting means to said adjusting means.
 14. A method ofcontrolling a detector array based optical system using light receivedby a detector array for machine vision from a plurality of succeedinglypresented objects comprising the steps of:detecting a lightcharacteristic of the light received by the detector array from apresented object during use; transmitting a signal indicative of thelight characteristic to a remotely located control system; and adjustinga light characteristic variable of the optical system for succeedingobjects when the received signal of at least one previous object isdeficient.
 15. A method of controlling an optical system as claimed inclaim 14 wherein the light characteristic variable is one of detectorarray scan rate, integration time, and light power output level of alight source.
 16. A method of controlling an optical system as claimedin claim 15 and further including the steps of initially operating themachine vision under sampling conditions to obtain sample lightcharacteristic values and thereafter setting the light characteristicvariables to accommodate these sampling values.
 17. A method oflinearizing the ouput of a detector array using a microprocessorcomprising the step of:setting up an element correction array in thememory of the microprocessor corresponding to the detector array;inputting precise object movement data to the microprocessor from anencoding device as an object is moved past the elements of the detectorarray; comparing the data from the encoder with the data from thedetector array at each array element and inputting an indication of thedifference between the two sets of data as offset values at thecorresponding positions in the element correction array; and during theoperating mode of the detector array, modifying the correspondingelement correction array offset value to each detector array elementreading to obtain a corrected detector array output which issubstantially linear.
 18. A method of linearizing as claimed in claim 17and further including the steps ofremoting the microcomputer from thedetector array; and transmitting the data to the microcomputer oversuitable transmission lines.
 19. A method of linearizing as claimed inclaim 18 and further including the step of periodically recalculatingthe offset values remotely by a signal from the microprocessor.
 20. Anapparatus for linearizing the output of a detector array comprising:amicroprocessor having a memory in which an element correction arraycorresponding to the detector array is set up; an encoding means forinputting precise object movement data to the microprocessor as anobject is moved past the elements of the detector array; a comparingmeans for comparing the data from said encoding means with the data fromthe detector array at each array element and for inputting an indicationof this difference between the two sets of data as offset values at thecorresponding positions in the element correction array; and a modifyingmeans for modifying the corresponding element correction array offsetvalve to each detector array element reading during operation to obtaina corrected detector array output which is substantially linear.
 21. Anapparatus for linearizing as claimed in claim 20 wherein saidmicroprocessor is remotely located from the diode array and furtherincluding a transmitting means for transmitting the data between themicroprocessor and the diode array.